Certain machining applications require drilling and/or reaming a hybrid stack-up of materials. A hybrid stack-up of materials may be defined as layers of discontinuous materials such as a stack-up of a carbon fiber composite, and titanium and/or aluminum, and/or steel. Machining such hybrid stack-ups can be time-consuming and can cause significant toolwear. An added challenge is to perform the drilling operation burrless, and chip free, to eliminate non-value added tasks such as cleaning and deburring the parts.
For example, certain aircraft require an aircraft wing made from a composite material, such as a graphite composite, be joined to a titanium section of an aircraft body with fasteners, such as without limitations, pins, bolts or rivets, that pass through holes made through the mating sections. The wing to body join task typically requires a three-step conventional drilling process comprising a pilot drill, followed by a step drill, followed by a finish diameter reamer. Each of these three steps can create messy spiraled chips, form elongated holes, and leave lubrication residue. Each step can also create ragged entry and exit burrs in the stack.
Dissimilar materials can also require dissimilar cutting tool characteristics. For example, machining titanium can require very tough tool characteristics while machining carbon fiber composites can require very wear resistant characteristics. Effective machining of dissimilar material can also require using separate tools having dissimilar tool geometry.
With all methods of drilling holes, the life of the cutting tool is severely shortened when drilling through hybrid stack-ups. With the three-step conventional drilling process, not only are the front cutting edges worn away, but also the diameter of the cutter is reduced, which prevents the drill from being resharpened and reused.
One process being explored as a one-step drilling solution for the wing to body join task is orbital hole machining. However, the life of the cutting tool used can be limited with orbital machining.
What is needed is a cutter to produce good quality holes in a hybrid stack-up without the shortcomings of current cutters.